Table is not flat

[wilkinswoodworking]

Today I ran some 60" molding that required moving the piece forward after machining half. When the profiles met in the center they were approximately 1/32" from lining up in plane. I did not think it was a big deal, just decided I needed to mill flat as I had not previously done that.
As soon as that process started I saw ridges being created by the back of the milling bit, I assumed the spindle was not perpendicular to the table as some others have posted but I decided to try the circular mill path. After finishing the milling I put a straight edge on the table in the y axis and found that my table was out 1/32" in the center all the way across the x axis. I also put the straight edge on the aluminum and it is out the same amount on both sides.
Does anyone else have this issue?
Are there adjustments that I am not aware of? 1/32 is not an acceptable amount of depth difference for the type of work I do.
Machine is an ar8 2x4'

[chuck26287]

Do I understand correctly that you performed the surface the spoilboard procedure to mill your spoilboard surface flat, you used the 1.5" mortising/flycut bit, and after that, when you placed a 2 foot straight edge along the 2 foot X axis, there was a 1/32" air gap in the middle of the table?

The extruded aluminum tables, or at least mine (AR8 Pro), aren't true. If I sight eye-level down the 4 foot length of the aluminum table, I can see very slight sag in the center. However, as long as this is a fixed and stable state, meaning it doesn't give and the sag doesn't change, surfacing the spoilbaords will make this table sag a mute point, as the new spoilboard surface will now be flat and perpendicular to the spindle axis. If your table is stable and not flexing, and your spoilboards are securely affixed to the table, then the only way to get a 1/32" dip in the center along the X axis is if your spindle is sagging down and back up as it travels across the gantry bridge, or your straight edge has an upward bow in it.

I would take a 2 foot level that you trust, with two true and parallel sides, and set it across the X-axis. This should be where you're seeing the 1/32" dip in the center of the table (air gap between spoilbaord surface and bottom edge/side of the level). Now I would manually bring my bit to the surface of the top side of the level on one side or the other of the X-axis. Then remove the level and move the spindle to the center of the X-axis. Then put the level back on the same way right up to the bit tip. Is it still right at the surface of the top side of the level, or is the bit tip now below the top surface of the level (showing the bit/spindle has dipped down at the center)?

Having looked pretty close at the manufacturing and actually having trammed and shimmed my AR8 spindle to improve the spindle perpendicularity, I can't imagine the gantry travel dropping that much at center. I would also be very surprised if a table was flexing that much. They're not perfectly flat, but they are pretty rigid.

Let us know what you find.

[Gordon]

There is no issue in the two foot direction. The table is sagging in the four foot direction. The gantry rides on rails that are attached to the table; therefore the spoil boards are showing ridges when cutting on the z axis.

[Gordon]

There is no issue in the two foot direction. The table is sagging in the four foot direction. The gantry rides on rails that are attached to the table; therefore the spoil boards are showing ridges when cutting on the z axis.

[chuck26287]

My mistake. I apologize. I read "my table was out 1/32" in the center all the way across the x axis" out of context. I re-read it and I see what you are saying now.